THE  UNIVERSITY 

OF  ILLINOIS 

LIBRARY 

580      < 
F452 

no- 1-10 


Return  this  book  on  or  before  the 
Latest  Date  stamped  below. 


University  of  Illinois  Library 


MM  26  J954 
rrr  -7  tSSl 


O  9  I  «1 


DEC  i  0  li 


L161— H4V 


'3*-^ 


FIGS 


-K« 


Wmm  OF  !LLW0!S  LIBRARY 

AUG  16  1922 


FIELD  MUSEUM  OF  NATURAL  HISTORY 

CHICAGO 
1922 


580 

FH5l 
no.  1-10 


m  is  1922 


5UTS5A4 


58- 
noJ-IQ 


Field  Museum  of  Natural  History 

DEPARTMENT  OF  BOTANY 
Chicago.  1922 

Leaflet  Number  1 


Fig: 


"The  wild  figs  upon  the  fig  trees  contain  a  creature 
called  psen :  this  is  at  first  a  little  worm,  and  afterwards 
having  ruptured  the  case  the  psen  flies  out.  and  leaves  it 
behind.  It  then  pierces  the  unripe  figs,  and  causes  them 
not  to  fall  off.  wherefore  gardeners  place  wild  fruit  near 
rhe  cultivated  kinds,  and  plant  the  wild  and  cultivated 
plants  near  each  other." — Arisrotle.  History  of  Animals. 
B.   V..   Ch.  XXVI  3. 

Botanically  the  figs  are  a  subdivision  of  the  mul- 
berry family.  They  are  peculiar  in  not  having  their 
flowers  exposed,  like  most  flowering  plants,  but  con- 
cealed within  a  hollow,  urn-shaped  receptacle  which 
has  precisely  the  appearance  of  a  young  fruit.  The 
apparent  absence  of  flowers  is  often  a  matter  for  com- 
ment. An  old  Chinese  writer  on  Materia  Medica  and 
Natural  History  in  discussing  the  fig  calls  it  the  "fruit 
without  flower."  In  reality  the  flowers  are  numerous 
but  insignificant  in  size  and  in  appearance.  All  other 
members  of  the  family  to  which  the  figs  belong  have, 
like  the  mulberry,  the  flowers  and  the  individual  fruits 
on  the  outside. 

Some  600  species  of  wild  figs  have  been  described 
to  date.  A  few  of  them  are  cultivated  or  well-known 
plants,  such  as  the  rubber  plant  which  in  its  normal 
habitat  is  a  rubber  yielding  tree,  the  Banyan  tree  which 
with  its  numerous  proproots  may  spread  over  an  acre 
or  more  of  ground,  and  the  sycamore  fig  that  furnished 
the  everlasting  wood  for  the  coffins  of  the  Pharaohs. 
The  vast  majority  of  figs,  however,  grow  in  semi-tropi- 
cal and  tropical  forests  and  jungles  as  shrubs,  trees,  or 


2  Field  Museum  of  Natural  History 

even  as  vines.  Two  species  grow  native  in  the  sub- 
tropical, southern  part  of  Florida.  One  of  them  is  a 
so-called  "strangling  fig."  These  begin  their  lives  as 
parasites  on  other  trees,  growing  at  first  much  like 
the  mistletoe,  but  eventually  sending  their  own  roots 
to  the  ground. 

The  cultivated  fig  (Ficus  carica)  is  a  native  of 
Semitic  Asia,  perhaps  particularly  of  southern  Arabia, 
but  occurs  also  in  Syria  and  in  Palestine.  Smyrna 
was  as  famous  for  its  figs  in  ancient  times  as  it  is  now. 
From  western  Asia  the  Phoenicians  and  later  the  Arabs 
carried  the  fig  throughout  the  entire  Mediterranean 
region.  The  old  Greeks  scoffed  at  the  barbarians  who 
did  not  have  figs  and  wine.  Romulus  and  Remus,  ac- 
cording to  tradition,  were  suckled  by  a  she-wolf  under 
a  fig  tree.  In  ancient  lore  the  fig  occupied  a  place  such 
as  does  our  more  familiar  apple  tree  of  the  Garden  of 
Eden.  Before  the  appearance  of  man,  figs  grew  in 
Europe  and  in  North  America.  Leaves  and  fruits  like 
those  of  the  cultivated  fig  have  been  found  fossil  in 
France.  With  the  Glacial  Period  the  fig  of  course  dis- 
appeared from  the  modern  temperate  zone  those 
which  now  grow  in  Europe  were  all  introduced  horti- 
culturally.  Figs  have  long  been  grown  in  China,  hav- 
ing been  brought  by  way  of  Persia  from  Asia  Minor. 
In  modern  times  the  cultivated  fig  has  been  introduced 
into  many  lands.  It  is  grown  in  South  and  Southwest 
Africa,  in  South  America,  and  in  Australia.  It  has 
been  grown  in  Sussex  in  England.  It  is  successfully 
cultivated  in  the  United  States,  especially  in  California 
and  in  the  Gulf  Region,  particularly  in  Texas.  In 
African  Sudan  where  the  fig  has  failed  to  grow  on  its 
<  iwn  roots,  it  has  been  grown  budded  on  the  more  trop- 
ical sycamore  fig. 

The  cultivated  fig  is  ordinarily  a  rapidly  growing 
small  tree  with  palmately  lobed  leaves  and  with  a  soft 

[2] 


Figs  3 

wood.  It  lives  sometimes  to  a  great  age  and  then 
reaches  large  dimensions.  It  may  be  uncommonly  pro- 
ductive and  is  said  to  bear  at  times  a  fruit  in  every 
leaf -axil,  though  part  of  such  a  huge  crop  is  apt  to  drop 
before  maturity. 

As  in  the  case  of  most  cultivated  fruits  there  are 
many  varieties.  Besides  the  common  fig,  called  mis- 
sion figs  in  California,  and  the  well-known  Smyrnas, 
a  California  writer  lists  Adriatic,  Eriocyne,  Cordelia, 
and  San  Pedro  figs.  The  popular  distinction  into  two 
kinds  is  on  the  basis  of  color,  purple  or  "black"  figs  and 
yellow  or  "white"  figs.  The  former  are  usually  less 
sweet  and  are  consumed  while  fresh.  The  figs  which 
come  dried  and  packed  in  boxes  or  "drums,"  such  as 
the  imported  Smyrna  figs,  are  of  the  white  variety. 
They  are  preserved  like  raisins  or  dates  by  their  own 
high  sugar  content. 

The  fig  fruit  is  a  hollow,  fleshy  receptacle,  with  a 
small  opening  or  "eye"  in  the  top  furnishing  the  only 
point  of  entry  to  the  interior  cavity.  Ordinarily  this 
opening  is  almost  entirely  closed  and  barred  on  the 
inside  by  a  zone  of  small,  interlocking  scales.  The 
inner  wall  of  the  receptacle  bears  the  very  numerous, 
small,  simple  flowers  which  in  the  edible  fig  are  all  of 
the  female  or  pistillate  kind,  more  or  less  perfect.  As 
these  grow  old  and  elongate,  they  completely  fill  the 
cavity.  Each  one  of  them  normally  matures  a  single 
small  dry  seed  which  in  some  cultivated  figs  is  always 
sterile,  in  others  fertile  when  the  flowers  have  been 
pollinated.  The  fruit  of  some  varieties  of  the  culti- 
vated fig  "ripens,"  i.  e.,  the  receptacle  becomes  soft, 
fleshy  and  edible,  without  pollination.  The  fruit  of 
others  will  not  ripen  unless  pollinated. 

Pollination  is  a  normal  occurrence  in  the  wild  fig 
only.  This,  in  contrast  to  the  edible  fig  {Ficus)  bears 
partly  inedible  fruit  and  is  known  as  the  goats-fig-tree, 

[3] 


4  Field  Museum  of  Natural  History 

" Capri ficus"  or  Caprifig.  It  is  also  known  as  the 
"male  fig"  because  its  figs  or  flower  receptacles  con- 
tain male  flowers  in  addition  to  the  others.  Female 
trees  of  the  wild  fig  also  exist  but  are  very  scarce. 
The  edible  fig  is  undoubtedly  derived  from  such.  The 
male  flowers  of  the  Caprifig  are  situated  in  the  upper 
part  of  the  fig  cavity,  immediately  below  the  scales, 
which  here  as  in  the  edible  fig,  bar  the  opening  to 
intruders. 

The  insect  which  ordinarily  inhabits  the  interior 
of  the  fig  cavity  is  the  minute  Fig  Wasp  (Blastophaga 
grossorum,  family  Chalcidae).  Through  the  course 
of  ages  of  association  (fossil  figs  have  been  found  in 
remains  of  the  Cretaceous  period)  the  life  history  of 
the  fig  and  of  the  minute  wasp  have  become  inextric- 
ably entangled.  Complete  interdependence  has  been  es- 
tablished between  them,  so  that  each  is  necessary  for 
the  existence  of  the  other.  Without  the  wasp  the  wild 
fig  would  soon  become  extinct,  for  there  would  be  no 
maturing  of  seed,  and,  vice  versa,  in  the  absence  of 
the  wild  figs  there  would  be  no  fig  wasps  hatching. 
The  female  fig  wasp  enters  the  young  caprifig  in  which 
at  a  certain  period  the  orifice  is  relaxed,  lays  its  eggs 
in  the  short-styled  flowers  near  the  base  of  the  cavity 
and  dies  within  the  fig.  These  flowers  are  known  as 
gall  flowers.  The  habit  of  response  to  the  visitations 
of  the  fig  wasp  has  proceeded  to  the  stage  of  anticipa- 
tion, for  gall  flowers  are  not  normal  flowers  that  be- 
come gall  flowers  through  the  egg-laying  of  the  insect, 
but  are  already  present  as  such,  though  barren  and 
useless  till  the  puncture  of  the  wasp  supplies  them  an 
inhabitant  in  the  shape  of  a  wasp  grub. 

The  eggs  hatch  into  male  and  female  wasps.  The 
small,  yellow,  wingless  males  mature  first,  bite  holes 
in  their  galls  and  crawl  out  into  the  cavity  of  the  fig. 
They  soon  cut  holes  in  the  gall  flowers  containing  the 

[4] 


Figs  5 

still  immature  females,  impregnate  them  and  shortly 
die  within  the  fig,  as  did  the  mother  wasp. 

Their  sisters,  the  female  wasps,  are  darker,  of  a 
brown  color  and  winged.  In  due  course  they  hatch 
and  immediately  set  about  leaving  the  cavity  of  the 
fig  within  which  there  is  no  room  for  them  to  spread 
their  wings.  To  reach  the  orifice  of  the  fig  they  must 
pass  the  male  flowers  and  become  dusted  with  the 
pollen  that  matures  at  the  very  time  of  their  hatching 
and  departure. 

Once  in  the  open  air  their  wings  soon  dry  and  each 
young  female  wasp  is  off  in  search  of  an  immature 
fig  in  which  to  deposit  eggs.  A  suitable  one  found,  the 
wasp  proceeds  to  cut  a  notch  in  one  of  the  outer  scales 
for  better  access,  then  makes  its  way  inside.  In  the 
process  the  wasp  generally  loses  its  wings.  These  are 
apt  to  stick  in  the  opening,  so  that  an  inhabitated  fig 
may  be  recognized  by  their  presence.  The  pollen  car- 
ried by  the  insect  is  brushed  off  on  the  stigmas  of  the 
long-styled  flowers  within.  Eggs  can  be  properly 
placed  only  in  figs  of  the  Caprificus  kind,  where  gall 
flowers  are  present. 

Both  the  wild  and  the  cultivated  fig  usually  bear 
three  crops  a  year.  As  insects  emerge  from  one  crop 
of  maturing  Caprifigs  they  ordinarily  find  green  fruit 
of  the  next  crop  ready  to  receive  them.  Each  crop  is 
thus  pollinated  with  pollen  of  the  preceding  crop.  An 
interval  of  about  two  months  elapses  between  the  en- 
trance of  the  egg-laying  fig  wasp  into  the  young  fig 
and  the  emergence  of  her  progeny  from  the  ripe  one. 
The  same  interval  of  time  separates  the  receptive  stage 
of  the  female  fig  flowers  and  the  ripening  of  the  pollen 
in  the  male  flowers,  completely  excluding  the  possibility 
of  self-pollination.  The  last  of  the  fig  wasps  of  the 
year  deposit  their  eggs  in  young  fruit  which  stays  on 
the  trees  until  spring. 

[5] 


6  Field  Museum  of  Natural  History 

To  prevent  the  dropping  of  fruit  of  the  edible  fig 
before  maturity,  it  is  an  ancient  practice  among  fig 
growers  to  hang  branches  of  the  wild  fig  tree,  or 
strings  of  ripe  Caprifigs,  in  the  trees  of  the  fig  orchard. 
The  fig  wasps  will  then  enter  the  young  edible  figs  and 
bring  about  pollination  with  the  Caprifig  pollen.  The 
true  Smyrna  fig  absolutely  requires  pollination  to  ripen 
its  fruit.  Fig  trees  of  this  variety  grown  in  Califor- 
nia continued  to  drop  their  immature  fruit  for  over 
twenty  years  till  the  wild  fig  with  its  fig  wasp  was 
introduced  and  the  so-called  "caprification"  was  made 
possible.  In  Mediterranean  countries  Caprifigs  for  the 
purpose  of  caprification  are  an  article  of  commerce 
at  times  bringing  a  higher  price  than  edible  figs.  It  has 
often  been  stated  on  apparently  good  botanical  author- 
ity that  the  practice  is  of  doubtful  utility.  According 
to  the  California  zoologist,  Eisen,  who  has  done  much 
to  clear  up  this  question,  the  confusion  is  due  to  a  fail- 
ure to  discriminate  between  the  varieties  which  require 
and  those  which  do  not  require  pollination  in  order  to 
mature  their  fruit.  The  latter  kind  are  grown  alto- 
gether in  some  localities,  as  in  southern  France. 

The  ancients  who  observed  the  fig  wasp  and  well 
knew  that  it  had  something  to  do  with  the  ripening  of 
the  fruit,  sought  to  account  for  it  in  accordance  with 
the  ideas  of  their  time.,  e.  g.,  "the  wasps  suck  up  the 
superfluous  humors,"  "they  enlarge  the  eye  and  per- 
mit the  fertilizing  air  to  enter." 

The  German  botanist,  Solms-Laubach  was  the  first 
to  investigate  thoroughly  the  flowers  of  the  fig  and 
extended  his  inquiries  to  some  of  the  numerous  species 
of  wild  Ficus.  Many  of  these  have  been  studied  since 
and  relations  have  been  found  to  exist  between  plant 
host  and  insect  tenant  similar  to  those  observed  in  the 
cultivated  fig.  The  insects  associated  with  the  wild 
figs  are  all  closely  related  to  the  fig  wasp  of  the  Capri- 

[«] 


Figs  7 

fig  but  distinct  and  different  in  the  various  species  of 
the  genus  Ficus.  It  would  seem  probable  that  most,  if 
not  all,  of  the  six  hundred  or  more  species  of  wild  figs 
throughout  the  world  are  as  dependent  for  their  con- 
tinued existence  on  their  respective  fig  wasp  guests  as 

is  the  Caprifig. 

B.  E.  Dahlgren. 


Exhibits  in  the  Field  Museum  pertaining  to  the  Mulberry 
Family  and  the  Fig  are  to  be  found  in  the  Department  of  Botany, 
Halls  28  and  29,  particularly,  a  reproduction  of  a  fruiting  branch 
of  the  Cultivated  Fig,  an  enlarged  section  of  a  young  flower 
receptacle,  an  enlarged  section  of  a  Caprifig  with  the  male  and 
female  Fig  Wasps,  wood  and  rubber  of  Ficus,  etc. 

In  the  Department  of  Geology,  Hall  18,  are  to  be  seen  fossil 
Figs,  of  the  Cretaceous  period,  from  Wyoming  and  Kansas. 


[7] 


*imsrry 
AUG 


16  )322 


